Use more caution to reduce spray drift


Tony Nye - OSU Extension



Before I get to the topic at hand, I thought I would let folks know about a Cover Crop Round Table Discussion to be held on Tuesday, July 23 beginning at 9 a.m. at the Fayette County Farm (2770 State Route 38).

This will be a non-formal discussion of cover crops from local farmers and Alan Sundermeier, OSU Extension Agent, Wood County. Sundermeier along with area farmers will share their experiences of using cover crops.

No RSVP is needed, just bring yourself and a willing to share and discuss the “hows and whys” of cover crops. If you have any questions contact Ken Ford, OSU Fayette County Extension Agent at 937-441-5762 or 740-335-1150.

It is hot and it has become dry and many sprayers have been out the past couple of weeks now. Now is a good time to remind growers about the potential for spray drift and how one can minimize drift.

Spray drift not only results in wasting expensive pesticides and pollution of the environment, it may damage non-target crops nearby, and poses a serious health risk to people living in areas where drift is occurring.

Drift happens! It accounts for about half of all non-compliance cases investigated by the Ohio Department of Agriculture.

According to Erdal Ozkan, Spray Technology specialist at Ohio State University, although complete elimination of spray drift is impossible, problems can be reduced significantly if you are aware of major factors which influence drift, and take precautions to minimize their influence on off-target movement of spray droplets.

The factors that play a role in either the creation, or reduction of spray drift are: a) Spray characteristics, such as volatility and viscosity of pesticide formulation; b) Equipment and application techniques used for spraying pesticides; c) Weather conditions at the time of application (wind speed and direction, temperature, relative humidity and stability of air around the application site); and most importantly, d) Operator care, attitude, and skill.

Ozkan provides five cost-effective things you can do to minimize spray drift.

Pay attention to wind speed more than anything else. The risk of spray drift will increase with increases in wind speed. There is no magic wind speed number below which drift will be minimum.

There are many other factors mentioned below that influence the wind speed you should stay under. Generally, wind speeds below 5 mph, coupled with other good management practices, will significantly reduce the injury caused by drift.

The best investment you can make is to buy a wind meter that tells you how high the wind velocity is at any given time. Having a wind meter handy will help you avoid a costly problem associated with spray drift.

Pay attention to wind direction. If the wind is blowing in the direction of some sensitive crops downwind, stop spraying. Don’t take the risk.

Come back later in the day or the next day when the direction of the wind has shifted away from the sensitive crops.

If you can, keep your nozzles as close to the target as possible while still producing a uniform distribution of spray on the target. This doesn’t cost any money as long as it is practical to make it happen.

When you’re ready to change nozzles, consider selecting nozzles that produce much fewer of the extremely small droplets that are most likely to drift away. Low-drift nozzles are in the market and do a tremendous job of eliminating extremely small, drift-prone droplets from the droplet spectrum.

This is especially important when spraying systemic chemicals like Glyphosate.

Since the active ingredients in these types of chemicals are translocated, not requiring a thorough coverage on the target weeds, there is no need to use small droplets that increases the risk of drift.

There are chemicals that are designed to increase the droplet size, and reduce the number of very small droplets when added into the spray mixture. Most of them are some sort of polymer that tends to increase the viscosity and density of the spray mixture which leads to larger droplets.

This, however, should be the last defense against drift. First consider the other options such as better targeting of the spray and switching to low-drift nozzles.

If you are using nozzles that produce relatively smaller droplets, avoid spraying under extremely hot and dry weather conditions. Under these conditions, evaporation of liquid from a droplet decreases its mass rapidly, increasing the drift distance of droplets.

Pay attention to conditions that may be conducive to formation of a phenomenon called thermal inversion. Normally, warm air rises up. So, during late morning to early evening, the surface temperature is usually warmer than the air temperature near the ground.

So, the small droplets discharged from a nozzle may follow this normal air movement from ground up, and eventually evaporate during this process.

However, during very early morning (before sunrise) or sometime after the sunset, the air temperature at some distance above the ground may be warmer than the ground temperature.

Under these conditions, the warm air above the ground is trapped between the ground and the inversion layer. Under these conditions, as shown in the picture below, the small droplets suspended in the air simply follow the horizontal air movement miles away from the application site.

So, avoid spraying during very early in the morning or very late in the evening, if the weather is extremely calm.

Tony Nye is the state coordinator for the Ohio State University Extension Small Farm Program and has been an OSU Extension Educator for agriculture and natural resources for over 30 years, currently serving Clinton County and the Miami Valley EERA.

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Tony Nye

OSU Extension